Science

Radiometric Dating of a Rock

Run Time: 00:04:30

Scientist Britt Argow talks with teacher Joe Reilly about how scientists can determine the approximate age of a rock: comparing the relative abundance of naturally-occurring radioactive elements to their decay products. Radioactive elements break down over time into another element at a known rate, called a "half-life." The "half-life" is the amount of time it takes for half of the radioactive element to change into another element. For example, in a given sample of rock, after 713 million years, half of the originally-present uranium-235 will be changed to lead: this is the "half-life" of uranium-235. After another 713 million years, half of what was left will have decayed, etc. By measuring the ratio of uranium-235 to lead, scientists can calculate the age of the rock. Featured Scientist: Carol de Wet, Ph.D.

Standards

NSES Standard

High School Standard D. Origin and Evolution of Earth System: Geologic time can be estimated by observing rock sequences at various locations. Current methods include using the known decay rates of radioactive isotopes present in rocks to measure the time since the rock was formed.